From their childhood, Catholics learn to pray the sign of the cross: “In the name of the Father, and of the Son, and of the Holy Spirit.” At Mass, the priest’s prayers frequently mention the Father, the Son, and the Spirit as well. The reason for this is that Catholics believe that God is not merely Unity (as all monotheists believe), but also Trinity. But what does this mean?
A Few Definitions
What we mean when we say that God is a Trinity is that there is one divine nature, one divine substance. A “substance” or “nature” is what something is. God, as a Trinity, exists in three Persons. A person is “who” someone is. In our experience, one human person each possesses one human nature. A husband and wife, no matter how closely united, are still two separate beings. In God, however, three Persons possess the same divine nature. If you were to ask each Person in the Trinity, “Who are you?” each person would answer something differently: “I am the Father;” “I am the Son;” “I am the Holy Spirit.” If you were to ask each Person, “Who are you?” you would get the same answer from each Person: “I am God.” Not, “I am a God,” as a human would say, “I am a human.” Rather, each divine Person, while not identical to the other divine Persons, is one in being with the other two divine Persons and is fully God. The word we use to describe this in the Nicene Creed is consubstantial. While we say in the Nicene Creed that the Son is consubstantial with the Father, it is also true that the Spirit is consubstantial with the Father and the Son.
Jesus Revealed the Trinity
Jesus’ life was the greatest revelation to us of God’s inner life. He claimed for Himself things that belonged only to God, like the power to forgive sins. His words and actions led the religious leaders of the time to believe he was a blasphemer, someone who shows a lack of reverence for God or who claims the attributes of God for himself. Yet Jesus also prayed to the Father and spoke to and about the Father as a separate Person. Jesus also promised to send the Holy Spirit to be with his disciples after he was no longer with them in his physical body (John 14:26). After Jesus’ death and resurrection and his ascension into heaven, early Christians understood that the Holy Spirit was also God. Yet Jesus was clear when he talked about the Holy Spirit that the Holy Spirit was someone other than himself or the Father.
Jesus was also clear that there is only one God, however. While he spoke to the Father as someone other than himself, he did also claim to be one with the Father. Jesus was the Messiah promised by the God of Israel, and that God was one God. Israel knew that there was only one God. Early Christians realized through what God had said through the Jewish prophets and through what Jesus said and did that God is one, but that God exists in three Persons.
The Doctrine Develops
During the first several centuries of Christian history, the Church encountered many different ways of thinking about God and about who Jesus was in relationship to the Father. The result of this was that the Church developed a more sophisticated language to talk about God. That is where we developed the use of the terms person and nature to make distinctions about God. The Nicene Creed, written at the Council of Nicea in 325 and revised at the Council of Constantinople in 381, was the result of the Church’s continued thinking about the Trinity. Catholics typically say the Nicene Creed at every Sunday Mass even over 1600 years later because the Trinity is so essential to the Christian faith.
Our earthly experience does not give us a lot of preparation for understanding the Trinity. When we meet other human beings, each human person possesses one human nature—there is only one nature per person and only one person per nature. Because the Trinity goes beyond our earthly experiences, analogies may be helpful in understanding it. On the other hand, any one analogy taken too far will not describe the Trinity accurately.
The story goes that St. Patrick used the shamrock to teach the Irish about the Trinity. That story may not be true, but the analogy is that just as there are three leaves on the shamrock, so there are three persons in God. This can be helpful in seeing that three things can also be one united thing. However, the Father, Son, and Spirit are not three parts of God.
Another analogy for the Trinity is that God is three in one, just as H2O can exist as a solid, a liquid, and a gas. This, too, can be helpful in understanding that there is something about God that is one and something about God that is threefold. However, ice, water, and vapor are three modes of being of H2O. To take this analogy too far would be to think that God exists in three modes and can express being God in three ways. However, the Father, Son, and Spirit are not just modes of being. We might say that this analogy emphasizes the oneness of God at the expense of God’s three-ness.
The family is a great analogy for the Trinity. The family is united in love, and the three Persons of the Trinity live in a relationship of love with one another. A pregnant mother contains another person within her, which is similar to how the Divine Persons cannot be separated from each other. The Holy Spirit is sometimes defined as the love between the Father and the Son, and when a husband and wife express their marital love, sometimes a new human person results. We even use the familial terms Father and Son to describe two Persons of the Trinity. However, this analogy also has its limits.
Obviously, a human family of three persons contains three separate human natures, not one. Furthermore, the human child begins to exist after his or her parents exist, whereas the Father, Son, and Holy Spirit are coeternal (meaning that each Person of the Trinity never began to exist and will never stop existing: God always exists, without beginning or end). We might say that this analogy emphasizes the three-ness of God at the expense of God’s oneness.
The Bible tells us, “God is love” (1 John 4:8). As a Trinity, the Father, Son, and Holy Spirit love one another completely and entirely. Love is truly the essence of God’s inner life. At times the Trinity may seem like a dull doctrine, but Jesus showed us this truth about who God is to reveal God’s inner life to us. God loves us and wants us to know him. God created us out of love, and we are created for love. We are created out of relationship for relationship. Faith in the Trinity, therefore, is not merely a doctrine but a dogma that shows us who God is and who we are as creatures made in his image.